Conventional rectifier circuits with capacitive output filters have relatively low power factors which limit the power that can be drawn from an ac line to a fraction of the rating of the line. Furthermore, highly distorted ac line currents are drawn by these conventional rectifiers, often causing interference with other electrical equipment in addition to equipment overcurrents and overvoltages. Techniques for improving power factor include passive waveform shaping methods, i.e. using input filters, and active methods, i.e. using boost or buck converter topologies. Such conventional active methods of obtaining high power factor generally employ a completely separate upfront converter to attain the high power factor followed by a dc-to-dc converter to produce the desired regulated dc output voltage. Thus, the power is converted twice, which is costly and inefficient. Moreover, the up-front converter must convert the entire delivered power. In fact, it must convert a peak power equal to twice the average power delivered.
A high power factor dc output power supply having only one power stage is described in commonly assigned, copending U.S. patent application of R.L. Steigerwald, Ser. No. 652,831, filed Feb. 8, 1991, which is incorporated by reference herein. The power supply of the Steigerwald patent application includes a dual-output switching converter having a first output coupled in series between a rectifier circuit and the input to the switching converter for providing a high power factor, and a second output for providing a regulated dc voltage at the power supply output. The first and second outputs are decoupled, resulting in a power supply capable of drawing high quality current waveforms from an ac source while producing a regulated dc output voltage with fast transient response. Furthermore, with the aforementioned Steigerwald power supply, high power factor is obtained without requiring a separate up-front power converter so that the power delivered by the supply does not have to be converted twice.
In addition to the hereinabove enumerated advantages of the high power factor power supply of the Steigerwald patent application, Ser. No. 652,831, cited hereinabove, it is also desirable to provide a high power factor, voltage-doubler rectifier for power conversion over a very wide input voltage range, e.g., applicable to both U.S. and European ac power sources. Conventional voltage-doubler rectifiers have poor power factor and relatively high harmonic distortion. Unfortunately, a practical solution is not to merely increase the boost voltage of the aforementioned Steigerwald power supply in order to offset a low input line voltage, because substantial circulating power, i.e., power greater than that delivered to the dc link, would result.